Researchers found unexpected biogeographical boundaries in Amazonia

During the 3-month expedition, the researchers lived on the ship that transported them from one inventory site to the next. Credit: Suomen Akatemia (Academy of Finland)

The new information necessitates revising the scenarios on how the enormous species richness in Amazonia has evolved and which factors define species distributions.

The general picture about Amazonia is that the rain forest is rather uniform, but large rivers form dispersal barriers that limit species distribution and trigger speciation, i.e. the evolutionary formation of new species. An international team led by researchers from the University of Turku, Finland, has identified a 1,000-kilometre-long boundary between two geological formations that constrains plant species occurrences more effectively than a large river.

"This boundary intrigued us, because it is so long. It is clearly visible in satellite images even though superficially the rainforests on both sides look similar. We decided to find out if there are floristic differences across the boundary, because the result would have a great impact on how we interpret Amazonian biogeography," explains Docent Hanna Tuomisto, who led the study.

"It is especially interesting that the newly documented boundary runs right across several large rivers. One of these is the Juruá, which has earlier been proposed to be a dispersal barrier," says Tuomisto.

Juruá is one of the largest tributaries of the Amazon river. The expedition documented species composition in the rainforest along more than 500 km of the river . Credit: Suomen Akatemia (Academy of Finland)

To document the ecological importance of the river and the boundary, Tuomisto organised an expedition to the Juruá River with researchers from Finland, Brazil and Denmark.

"We lived on a river ship for three months. At daytime, the ship was parked at the shore while we were in the forest making plant inventories and collecting soil samples. Each night we returned to the ship, and by the next morning it took us to the next field site," tells Gabriel Moulatlet, a Brazilian botanist and a doctoral candidate at the University of Turku.

Already in the field it became obvious that the geological boundary separated two, floristically very different forest areas from each other. Most of the plant species registered by the team were either completely restricted to only one side of the boundary or were much more abundant on one side than the other.

Laboratory analyses confirmed that also soils on the two sides were different. In addition to affecting present-day species distributions, the boundary may therefore have promoted speciation, as plants on opposite sides have been gradually adapting to different kinds of soils.

Usually rivers have been thought to be the most important dispersal barriers in Amazonian rain forests. Therefore, many species distribution maps have been drawn in a way that their limits follow rivers. These limits are uncertain, however, because Amazonia is poorly known: there is little information on where species actually occur.

"Our findings raise the question: how common are such boundaries in Amazonia? This is what we would like to find out next, as it is otherwise impossible to understand and map Amazonian biodiversity," says Docent Kalle Ruokolainen, another contributor to the study.

The research was funded by the Academy of Finland, Danish National Research Council and the Brazilian National Council for Scientific and Technological Development.

Related Stories

A mysterious line where two millipede species meet has been mapped in northwest Tasmania, Australia. Both species are common in their respective ranges, but the two millipedes cross very little into each other's territory. ...

A study reveals how little we know about the Amazonian diversity. Aiming to resolve a scientific debate about the validity of two species of freshwater shrimp described in the first half of the last century, researchers have ...

An international team of researchers is challenging a commonly held view that explains how so many species of birds came to inhabit the Neotropics, an area rich in rain forest that extends from Mexico to the southernmost ...

From above the Amazon rainforest may look like an endless, uniform sea of greenery, but it turns out there are sharp lines through it separating very different ecosystems with distinct inhabitants. And these lines are drawn ...

Amazonia's huge biodiversity originated with the formation of the Andes and, as such, dates back further than previously realised, claims an article written by an international research group, headed by a researcher from ...

The pre-Columbian settlements in Amazonia were not limited to the vicinities of rivers and lakes. One example of this can be found in the Santarém region in Brazilian Amazonia, where most archaeological sites are situated ...

Constituting over 78 % of the air we breathe, nitrogen is the element found the most often in its pure form on earth. The reason for the abundance of elemental nitrogen is the incredible stability and inertness of dinitrogen ...

Off the coast of Washington, columns of bubbles rise from the seafloor, as if evidence of a sleeping dragon lying below. But these bubbles are methane that is squeezed out of sediment and rises up through the water. The locations ...

The dramatic difference in gonad size between honey bee queens and their female workers in response to their distinct diets requires the switching on of a specific genetic program, according to a new study publishing March ...

An international team based in Ghent, Belgium (VIB-UGent Center for Plant Systems Biology) and Basel, Switzerland (University of Basel), found a link between a class of enzymes and immune signals that is rapidly triggered ...

New photonic tools for medical imaging can be used to understand the nonlinear behavior of laser light in human blood for theranostic applications. When light enters biological fluids it is quickly scattered, however, some ...

One of the ocean's little known carnivores has been allocated a new place in the evolutionary tree of life after scientists discovered its unmistakable resemblance with other sea-floor dwelling creatures.

0 comments

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.